An electromagnetic actuator for opening and closing a valve of an internal combustion engine generally includes an electromagnet for producing an electromagnetic force on an armature. The armature is neutrally-biased by opposing first and second return springs and coaxially coupled with a cylinder valve stem of the engine. In operation, the armature is held by the electromagnet in a first operating position against a stator core of the actuator. By selectively de-energizing the electromagnet, the armature may begin movement towards a second operating position under the influence of a force exerted by the first return spring. Power to a coil of the actuator is then applied to move the armature across a gap and begin compressing the second return spring.
As can be appreciated by those skilled in the art, it is desirable to closely balance the spring force on the armature with the magnetic forces acting on the armature in the region near the stator core so as to achieve a near-zero velocity "soft landing" of the armature against the stator core. In order to obtain a soft-landing of the armature against the stator core, power may be removed from the coil as the armature approaches the stator in the second position. The stator coil may then be re-energized, just before landing the armature, to draw and hold the armature against the stator core. In practice, a soft landing may be difficult to achieve because the system is constantly being perturbed by transient variations in friction, supply voltage, exhaust back pressure, armature center point, valve lash, engine vibration, oil viscosity, tolerance stack up, temperature, etc.
Experimental results for particular engines and actuator arrangements indicate that to achieve quiet actuator operation and prevent excessive impact wear on the armature and stator core, the landing velocity of the armature should be less than 0.04 meters per second at 600 engine rpm and less than 0.4 meters per second 6,000 engine rpm. In order to achieve these results under non-ideal conditions (e.g., the harsh environment of an internal-combustion engine), it is necessary to dynamically adjust the magnetic flux generated within the stator core to compensate for variations in operating voltage, friction within the actuator, engine back-pressure and vibration, during every stroke of the armature. External sensors, such as Hall sensors, have been used to measure flux in electromagnetic actuators. However, sensors have proven to be too costly and cumbersome for practical applications.
Thus, a need exists for a sensorless control system and method for an electromagnetic actuator capable of dynamically compensating for non-ideal disturbances that exist in and near internal combustion engines. Further, a need exists for a high-speed sensorless control system and method for an electromagnetic actuator capable of detecting and compensating for the above-described non-ideal conditions during each stroke cycle of the armature.